Add a instance lookup helper to v3 plugins.

There was a lot of duplicated error checking code in the v3 plugins
around instance lookup via the compute API. I've created a generic
helper to do this, and then moved all the existing plugins across to
using that helper. This reduces the amount of duplicated code in
these plugins.

Change-Id: I52c15da0499eda676225603d5a0b2739875d1fca
Remove @author from copyright statements.

We have git to track authorship, so let's not pad source files
with it as well.

Co-authored-by: Joe Gordon <joe.gordon0@gmail.com>

Change-Id: Ic2d62d6743f7716c086749cd99922b6c496771d4
Refactor stats to avoid bad join

Refactor compute node methods to remove slow join with compute node
stats.  Stats are encoded instead in a single json/text column.

Implements: blueprint compute-node-stats-as-resource-tracker-extension

Change-Id: I1651d758dd21c87ccd768fdd86c910ec5080c71c
Merge "Remove @author from copyright statements."
Merge "Add a instance lookup helper to v3 plugins."
Merge "Refactor stats to avoid bad join"
Merge commit 'refs/changes/97/66597/4' of git://gold.eng.hq.xensource.com/git/github/openstack/nova into tmpbranch